Electrically-heated glowplug and method for production of an electrically-heated glowplug

ABSTRACT

An electrically heatable glow plug and a method of manufacturing an electrically heatable glow plug allow better decoupling between a heating coil and a combustion-chamber-side end of a glow tube. The electrically heatable glow plug for internal combustion engines includes a metallic glow tube, sealed on the combustion-chamber side, into which an electrically conductive heating coil is introduced, the heating coil being connected in an electrically conductive manner to the glow tube in the region of the sealed combustion-chamber-side end of the glow tube. A sealing arrangement is provided which seals the glow tube on the combustion-chamber side and supports the heating coil and only protrudes into the heating coil if the heating coil is connected to the sealing arrangement via an inner side of the heating coil, for which purpose the sealing arrangement is in contact with the inner side of the heating coil essentially over the entire length protruding into the heating coil.

FIELD OF THE INVENTION

[0001] The present intention is directed to an electrically heatable glow plug and a method for manufacturing an electrically heatable glow plug.

BACKGROUND INFORMATION

[0002] An electrically heatable glow plug for internal combustion engines, which includes a glow element having a corrosion-resistant sealed metal sheath, a filling contained therein made of an electrically non-conductive, compressed powder, and an electrically conductive heating coil and regulating coil embedded in the filling, is referred to in German Patent Application No. 197 56 988. In this case, one end of the heating coil is welded in an electrically conductive manner to the tip of the metal sheath.

[0003] The heating coil has been provided with multiple centering turns on its combustion-chamber side. The turns are then inserted into a corresponding hole on the combustion-chamber-side end of the glow tube. Subsequently, the heating coil is welded directly to the glow tube on the combustion-chamber-side end of the glow tube and the glow tube is thus sealed. A TIG welding method (tungsten-inert gas) may be used for this purpose.

[0004] The disadvantage of this technique may be that the number of turns of the heating coil welded to the glow tube is not defined. As a result, the resistance of the heating coil varies and therefore both the heating characteristic and the temperature of the glow plug vary.

[0005] If the heating coil and the glow tube are made of different materials, the further disadvantage may result that two different materials must be welded to one another on the combustion-chamber-side end of the glow tube. This results in the glow tube and the heating coil losing their original properties due to the mixing of the two materials in the welded region. The glow tube may crack at this point during continuous operation of the glow plug. Air then enters the glow tube. This may result in oxidation of the heating coil material and the regulating coil material and therefore inevitably in the malfunction of the glow plug.

[0006] A rod glow plug, which includes a glow tube, an internal heating coil, and possibly a regulating coil and a connection terminal leading into the glow tube, is referred to in European Patent Application 1 030 111. The coils are connected to the connection terminal and to the tip of the glow tube. A stabilizing rod is provided, which extends during an assembly step from the connection terminal up to the tip of the glow tube, and possibly into or through an opening in the tip of the glow tube. The stabilizing rod runs essentially centrally through the coils.

SUMMARY OF THE INVENTION

[0007] The electrically heatable glow plug according to the present invention and the exemplary method of manufacturing an electrically heatable glow plug according to the present invention include a sealing arrangement to seal the glow plug on the combustion-chamber side and supports the heating coil. It only protrudes into the heating coil if the heating coil is attached to the sealing arrangement via an inner side of the heating coil. For this purpose, in this case the sealing arrangement is in contact with the inner side of the heating coil essentially over the entire length protruding into the heating coil. In this manner, the heating coil is not connected directly to the glow tube, but rather indirectly via the sealing arrangement. Therefore, the procedures of sealing the glow tube and of connecting the heating coil to the glow tube in an electrically conductive manner may be separated from one another. The glow tube is then sealed by the sealing arrangement independently of the heating coil, so that the sealing procedure of the glow tube has no influence on the resistance of the heating coil. This resistance may be set significantly more exactly by definitely connecting the heating coil to the sealing arrangement beforehand, i.e., before introduction of the heating coil into the glow tube, the connection of the heating coil to the sealing arrangement only serving for the electrical contact between the heating coil and the sealing arrangement, but has no sealing function.

[0008] A further advantage is that a stabilizer rod is not necessary, so that material and assembly costs are saved.

[0009] Advantageous refinements of the exemplary glow plug and the exemplary method of manufacturing the glow plug according to the present invention are described herein.

[0010] An especially precisely set resistance of the heating coil is obtained if the heating coil is connected to the sealing arrangement by at least one defined welded point. A somewhat more stable connection between the heating coil and the sealing arrangement, also having higher precision of the resulting resistance of the heating coil, is obtained if the heating coil is connected to the sealing arrangement by a continuous weld seam. A defined resistance of the heating coil may also be set by crimping the heating coil to the sealing arrangement, this connection technique being especially simple and simultaneously saving material and energy.

[0011] It may be especially advantageous if the sealing arrangement is a metallic sealing arrangement, in particular from the same material as the glow tube. If the sealing arrangement is produced from the same material as the glow tube, different materials do not have to be welded when the glow tube is sealed, so that the glow tube is much more resistant to cracks at this point during long-term operation of the glow plug. This has a positive effect on the corrosion properties of the glow tube tip, since the tip does not include a component of the heating coil material. The glow plug according to the present invention therefore may have a significantly increased service life.

[0012] It may be advantageous if the sealing arrangement is implemented as a cap which covers the glow tube on the combustion-chamber side and simultaneously has an elevation on the glow tube side which receives the heating coil. In this manner, the heating coil may be placed as far forward as possible in the region of the combustion-chamber side tip of the glow tube, so that the point of most intense heating extends as close as possible to the tip of the glow tube.

[0013] A further advantage results if the sealing arrangement has a pin on the combustion-chamber side which protrudes into an opening of the glow tube on the combustion-chamber side and seals it, and if the sealing arrangement includes a base on the glow tube side in which the heating coil is embedded. In this manner, the glow tube may be sealed in an especially simple, stable, and permanent manner on the combustion-chamber side.

[0014] It may be especially advantageous if the base has a first projection on the glow tube side which protrudes into the heating coil and is in contact with the inner side of the heating coil on the combustion-chamber-side end. The position of the heating coil is defined precisely in this manner.

[0015] It may also be advantageous if the base itself protrudes into the heating coil and is in contact with the inner side of the heating coil on the combustion-chamber-side end. In this manner, the material for a projection on the base on the glow tube side may be saved.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016]FIG. 1 shows a first exemplary embodiment of a glow plug according to the present invention.

[0017]FIG. 2 shows a second exemplary embodiment of a glow plug according to the present invention.

[0018]FIG. 3 shows a third exemplary embodiment of a glow plug according to the present invention.

[0019]FIG. 4 shows a fourth exemplary embodiment of a glow plug according to the present invention.

[0020]FIG. 5 shows a fifth exemplary embodiment of a glow plug according to the present invention.

DETAILED DESCRIPTION

[0021] In FIG. 1, 1 identifies a glow plug, which is implemented as a sheathed-element glow plug, for example, and includes a plug body 85. Plug body 85 includes a thread 90 to be screwed into a cylinder head of an internal combustion engine. A glow tube 10 is pressed into plug body 85 on the combustion-chamber side. On the combustion-chamber side, glow tube 10 includes a heating coil 15 and a regulating coil 95 adjoining it, which is connected to heating coil 15. Glow tube 10 protrudes on the combustion-chamber side into a combustion chamber 5 of the cylinder head in the region of heating coil 15. Regulating coil 95 is in contact with a terminal stud 100, which protrudes out of plug body 85 on the end distal from the combustion chamber and may be connected to a positive terminal of the vehicle battery.

[0022] Terminal stud 100 and glow tube 10 are sealed in plug body 85 against environmental influences by a sealing ring 105. On the end distal from the combustion chamber, plug body 85 has a hexagon 110, with the aid of which the glow plug may be screwed into the cylinder head and/or unscrewed from the cylinder head using a torque tool. A double seal 115 seals the inside of plug body 85 from environmental influences on the end of plug body 85 distal from the combustion chamber and an adjoining insulating disk 116 electrically insulates plug body 85 from terminal stud 100. Sealing ring 105 also electrically insulates terminal stud 100 from plug body 85. Sealing ring 105 and double seal 115, as well as insulating disk 116, are made of a plastic or elastomer, for example.

[0023] Double seal 115 and insulating disk 116 are fixed via a round nut 117, or alternatively a round plug. Round nut 117 or the round plug may be screwed and caulked or only caulked. Insulating powder filling made of magnesium oxide, for example, which electrically insulates heating coil 15 and regulating coil 95 from glow tube 10, is poured into glow tube 10.

[0024] The combustion-chamber-side end of glow tube 10 is identified in FIG. 1 with reference number 20. In this case, glow tube 10 is implemented as tubular and is terminated on the end distal from the combustion chamber by terminal stud 100 and sealing ring 105. On the combustion-chamber side, glow tube 10 is sealed by a sealing arrangement 25. Inside glow tube 10, sealing arrangement 25 supports heating coil 15. Glow tube 10 is implemented as a metallic glow tube. Sealing arrangement 25 is also implemented as a metallic sealing arrangement. In this case, sealing arrangement 25 and glow tube 10 may be made of the same metal. The connection between sealing arrangement 25 and glow tube 10 may be implemented by a welded connection, for example. Plug body 85 is also implemented as a metallic plug body.

[0025] In this manner, sealing arrangement 25, glow tube 10, and plug body 85 form an electrical reference potential, the vehicle frame, for example. If terminal stud 100 is connected to the positive terminal of the vehicle battery, a current flows through regulating coil 95 and heating coil 15 via terminal stud 100 up to the vehicle frame. In this manner, heating coil 15 is heated and heats glow tube 10 in combustion chamber 5 in order to initiate the combustion process. Regulating coil 95 is made of a material having a resistance which has a positive temperature coefficient, a cobalt-iron alloy, for example. Heating coil 15 is made of a material having an electrical resistance which is as independent of temperature as possible. Heating coil 15 may be made of an iron-chromium-aluminum alloy, for example. Due to the fact that heating coil 15 is embedded in sealing arrangement 25, an electrically conductive connection between heating coil 15 and sealing arrangement 25 is ensured.

[0026] Heating coil 15 may be connected to sealing arrangement 25 by one or more weld points. Alternatively, heating coil 15 may be connected to sealing arrangement 25 by a continuous weld seam. In another alternative, heating coil 15 may be connected to sealing arrangement 25 by crimping. In all three cases, a precisely defined number of turns of heating coil 15 may be connected to sealing arrangement 25 and to produce a precisely defined electrical resistance of heating coil 15 in this manner. As shown in FIG. 1, precisely one turn, specifically the last turn of heating coil 15 facing combustion chamber 5, is connected to sealing arrangement 25, while the remaining turns of heating coil 15 are not connected to sealing arrangement 25 and therefore produce the electrical resistance of heating coil 15.

[0027] Heating coil 15 is thus not connected directly to glow tube 10, but rather is connected indirectly via sealing arrangement 25. No portions of heating coil 15 are therefore present in the welded connection between sealing arrangement 25 and glow tube 10.

[0028] Since the welded connection between sealing arrangement 25 and glow tube 10 now does not contain any portions of heating coil 15, it should be less susceptible to nitridation and corrosion, so that no cracks may arise in the region of this welded connection, which might in turn result in air and gas penetrating into the inside of glow tube 10 and therefore also to heating coil 15 and to regulating coil 95. Therefore, glow plug 1 has a significantly longer service life and has a precisely defined resistance of heating coil 15.

[0029] Sealing arrangement 25 may, of course, be made of a different material than glow tube 10. However, this material is not to include the material of heating coil 15, in order to prevent the above-described susceptibility to corrosion and nitridation in the welded connection between sealing arrangement 25 and glow tube 10.

[0030] The welded connection between sealing arrangement 25 and glow tube 10 may be implemented by a TIG welding method (tungsten-inert gas), for example. The welding of heating coil 15 to sealing arrangement 25, if a welded connection is provided here, may be performed using an especially precise laser welding method, for example, since a reliable electrical connection is especially important here.

[0031] Since the seal of glow tube 10 by sealing arrangement 25 and the welded connection described between sealing arrangement 25 and glow tube 10 are produced independently of heating coil 15, they also have no influence on the resistance of heating coil 15. The different welds resulting between sealing arrangement 25 and glow tube 10 then no longer have an effect on the resistance of heating coil 15, since they are completely embedded in sealing arrangement 25. For this purpose, the region in which heating coil 15 is embedded in sealing arrangement 25 is separated completely from the region in which sealing arrangement 25 is connected and/or welded to the glow tube. This should apply to all of the exemplary embodiments described here.

[0032] In the first exemplary embodiment shown in FIG. 1, sealing arrangement 25 is implemented as a cap which completely covers glow tube 10 on the combustion-chamber side. On the glow tube side, sealing arrangement 25 includes an elevation 30, in the form of one or more pins or a continuous ring, for example. Outer side 35 of elevation 30 is in contact with an inner wall 40 of glow tube 10. Heating coil 15 is embedded in inner side 45 of elevation 30. For this purpose, it is sufficient if the last turn of heating coil 15, which faces combustion chamber 5, is clamped in elevation 30, which is facilitated particularly if an annular elevation is used. In addition, this turn of heating coil 15 may also be welded to elevation 30 by a continuous weld seam or individual, small, defined welding points, using a laser welding method, for example.

[0033] In this manner, the region of the connection of sealing arrangement 25 to glow tube 10 is separated from the region where heating coil 15 is embedded in sealing arrangement 25, as required. Through the arrangement shown in FIG. 1, heating coil 15 is brought very close to the combustion-chamber-side end of sheathed-element glow plug 1, so that the point of most intense heating of heating coil 15 and therefore of glow tube 10 protrudes as far as possible into combustion chamber 5.

[0034] During assembly of sheathed-element glow plug 1, heating coil 15 is first connected on the combustion-chamber side to sealing arrangement 25 in the manner described and subsequently introduced, in the direction of the arrow as shown in FIG. 1, into glow tube 10 from the combustion-chamber-side end of glow tube 10 together with sealing arrangement 25 and regulating coil 95, which is attached to heating coil 15 on the end distal from the combustion chamber, until sealing arrangement 25 presses against the combustion-chamber-side end of glow tube 10. Subsequently, sealing arrangement 25 is connected to glow tube 10 by welding, for example.

[0035] During the welding of sealing arrangement 25 to glow tube 10, heating coil 15 and regulating coil 95 may be held centered in relation to glow tube 10 on the end of glow tube 10 distal from the combustion chamber by a suitable support device. In this manner, contact of heating coil 15 and regulating coil 95 with glow tube 10 is avoided and centered attachment of terminal stud 100 to regulating coil 95 is made possible. During the welding of sealing arrangement 25 to glow tube 10, these two parts may be rotated by 360 degrees in order to achieve a uniform weld seam. In FIG. 1, sheathed-element glow plug 1 is shown in a longitudinal section. In this case, sealing arrangement 25 and glow tube 10 may be configured to be rotationally symmetric.

[0036] A second exemplary embodiment of sheathed-element glow plug 1 according to the present invention is shown in FIG. 2, identical reference numbers identifying identical elements as in FIG. 1. In this case, only a combustion-chamber side section of glow tube 10 is shown for reasons of clarity, again as a longitudinal section. In contrast to the first exemplary embodiment shown in FIG. 1, in the second exemplary embodiment shown in FIG. 2, glow tube 10 is not completely open on its combustion-chamber-side end 20, but rather has only a comparatively small opening 55, which is implemented as a bore hole, for example. The bore hole is positioned approximately on the combustion chamber tip of glow tube 10.

[0037] Sealing arrangement 25 is implemented as a plug, which has a pin 50 on the combustion-chamber side, in this exemplary embodiment. Pin 50 protrudes into combustion chamber opening 55 of glow tube 10 and seals it completely. On the glow tube side, sealing arrangement 25 includes a base 60 whose diameter is greater than the diameter of opening 55 and in which heating coil 15 is embedded. In this case as well, heating coil 15 is first connected to regulating coil 95 and sealing arrangement 25. Regulating coil 95 is also distal from the combustion chamber and is caulked to terminal stud 100, as shown in FIG. 1. Subsequently, the arrangement thus formed is introduced as shown by the direction of the arrow in FIG. 2, with sealing arrangement 25 in front, into glow tube 10 via the opening of glow tube 10 distal from the combustion chamber, until pin 50 protrudes into opening 55 of glow tube 10. Subsequently, pin 50 of sealing arrangement 25 is welded to glow tube 10 in the region of opening 55.

[0038] In this case as well, the glow tube may be rotated by 360 degrees during the welding process while pin 50 of sealing arrangement 25 is inserted in opening 55. The TIG welding method may be used again. This principle of the attachment of sealing arrangement 25 to glow tube 10 is also the basis of the further exemplary embodiments; which are described in the following. They differ only in the attachment of heating coil 15 to a base 60. Thus, base 60 according to the second exemplary embodiment shown in FIG. 2 includes a first projection 65, which protrudes into heating coil 15 and is in contact with inner side 70 of heating coil 15 on its combustion-chamber-side end.

[0039] In this case, as shown in FIG. 2, only the last turn of heating coil 15 on the combustion-chamber side is again connected to first projection 65. Base 60 has a larger diameter than first projection 65 in this case, so that the last turn of heating coil 15 on the combustion-chamber side also rests on base 60 and heating coil 15 is therefore separated completely by base 60 from the welded connection to be formed between pin 50 and glow tube 10. A component of the heating coil material is thus again prevented from being contained in the connection between pin 50 and glow tube 10, i.e., between sealing arrangement 25 and glow tube 10. A direct connection between heating coil 15 and glow tube 10 is avoided in this manner, so that the advantages connected therewith, which have already been described, are achieved.

[0040] The material for sealing arrangement 25 may be selected in accordance with the first exemplary embodiment shown in FIG. 1. The connection of heating coil 15 to sealing arrangement 25 may also be produced, as in the first exemplary embodiment, by one or more welded points, by a continuous weld seam, or by crimping the combustion-chamber-side end of heating coil 15 to first projection 65.

[0041] Therefore, a precisely defined connection of only the last combustion-chamber side turn of heating coil 15 to sealing arrangement 25, for example, and therefore a precisely defined resistance of heating coil 15, may also be implemented in the second exemplary embodiment shown in FIG. 2. Of course, the connection may also include more than one turn of heating coil 15, but in any case it includes a precisely defined number of turns, which may be predetermined and implemented exactly. In this case, a thread may be provided on the first projection for screwing on heating coil 15.

[0042] A third exemplary embodiment is shown in FIG. 3, in which identical reference numbers identify identical elements as in the preceding exemplary embodiments. As described, the connection of sealing arrangement 25 to glow tube 10 is identical in the third exemplary embodiment to that in the second exemplary embodiment shown in FIG. 2. Only the attachment of heating coil 15 to base 60 is different. As shown in FIG. 3, base 60 includes a second projection 75 on the glow tube side, which encloses outer side 80 of a defined number of turns of heating coil 15 on its combustion-chamber-side end. In this manner, heating coil 15 may be attached identically to the first exemplary embodiment shown in FIG. 1, base 60 and second projection 75 not contacting glow tube 10 laterally as shown in FIG. 3.

[0043] In the third exemplary embodiment shown in FIG. 3, as in the second exemplary embodiment shown in FIG. 2, heating coil 15 is also separated from glow tube 10 by base 60 of sealing arrangement 25, whose diameter is larger than the diameter of heating coil 15 and which encloses heating coil 15 through second projection 75. In this case, second projection 75 may be implemented similarly to elevation 30 of the first exemplary embodiment shown in FIG. 1.

[0044] A fourth exemplary embodiment of the present invention is shown in FIG. 4, in which identical reference numbers again identify identical elements as in the preceding figures. In this case, the connection between sealing arrangement 25 and glow tube 10 is implemented in the same manner as in the second exemplary embodiment shown in FIG. 2. Only the attachment of heating coil 15 to base 60 is different. In this case as well, the diameter of base 60 is larger than the diameter of pin 50, as in the second and third exemplary embodiments, so that base 60 projects completely beyond pin 50 on the glow tube side. In this case, base 60 itself protrudes into heating coil 15 and is in contact with inner side 70 of heating coil 15 on the combustion-chamber-side end.

[0045] Therefore, in the fourth exemplary embodiment, base 60 assumes the function of first projection 65 in the second exemplary embodiment, so that a projection for the attachment of heating coil 15 may be dispensed with. The last turn of heating coil 15 on the combustion-chamber side rests on glow tube 10 in this case, but outside opening 55 having pin 50, so that during welding of pin 50 to glow tube 10 in opening 55, no material of heating coil 15 is included in the welded connection, and heating coil 15 is separated completely by base 60 from the welded connection between pin 50 and glow tube 10 in this manner.

[0046] In the fourth exemplary embodiment shown in FIG. 4, the last two turns of heating coil 15 on the combustion-chamber side are connected to base 60 by one or more welded points, by a continuous weld seam, or by crimping or a screw joint, for example. A defined, predetermined resistance of heating coil 15 may also be set in this manner. In the fourth exemplary embodiment shown in FIG. 4, heating coil 15 may be positioned as far as possible into the region of the tip of glow tube 10, so that the point of most intense heating of glow tube 10 protrudes as much as possible into combustion chamber 5.

[0047] A fifth exemplary embodiment is shown in FIG. 5, in which identical reference numbers again identify identical elements as in the preceding exemplary embodiments. In this case, the connection between sealing arrangement 25 and glow tube 10 is identical to that in the second exemplary embodiment shown in FIG. 2 and only the attachment of heating coil 15 to base 60 is achieved differently. In the fifth exemplary embodiment shown in FIG. 5, heating coil 15 merely rests on base 60 on the glow tube side, and is therefore separated from the connection between pin 50 and glow tube 10 by base 60, whose cross-section is larger than that of pin 50, so that no portion of the heating coil material may enter the welded connection of pin 50 to glow tube 10.

[0048] The connection between heating coil 15 and base 60 is now again produced on the last combustion-chamber side turn of heating coil 15 by one or more welded points or a continuous weld seam. In this manner, the resistance of heating coil 15 may be set to a defined, predetermined value. In this embodiment, as in the fourth embodiment shown in FIG. 4 and the second embodiment shown in FIG. 2, no elevation and no projection of sealing arrangement 25 is attached between heating coil 15 and the lateral wall of glow tube 10.

[0049] Sealing arrangement 25 only protrudes into heating coil 15 for the case in which heating coil 15 is attached to sealing arrangement 25 via inner side 70 of heating coil 15, for which sealing arrangement 25 is in contact with inner side 70 of heating coil 15 essentially over the entire length protruding into heating coil 15. 

What is claimed is:
 1. An electrically heatable glow plug (1), in particular a sheathed-element glow plug, for internal combustion engines, having a metallic glow tube (10), which is closed on the combustion-chamber side, and into which an electrically conductive heating coil (15) is introduced, the heating coil (15) being connected in an electrically conductive way to the glow tube (10) in the region of the closed, combustion-chamber-side end (20) of the glow tube (10), wherein a sealing means (25) is provided, which seals, on one hand, the glow tube (10) on the combustion-chamber side and supports, on the other hand, the heating coil (15), and only protrudes into the heating coil (15) if the heating coil (15) is connected to the sealing means (25) via an inner side (70) of the heating coil (15), for which purpose the sealing means (25) is, in this case, essentially in contact with the inner side (70) of the heating coil (15) over the entire length protruding into the heating coil (15).
 2. The glow plug (1) as recited in claim 1, wherein the heating coil (15) is connected to the sealing means (25) by at least one welded point, by a continuous welded seam, or a screw joint, or by crimping.
 3. The glow plug (1) as recited in claim 1 or 2, wherein the sealing means (25) is metallic, in particular of the same material as the glow tube (10).
 4. The glow plug (1) as recited in claim 1, 2, or 3, wherein the sealing means (25) is welded to the glow tube (10).
 5. The glow plug (1) as recited in one of the preceding claims, wherein the sealing means (25) is designed as a cap, which covers the glow tube (10) on the combustion-chamber side and includes a glow-tube-side elevation (30), which receives the heating coil (15).
 6. The glow plug (1) as recited in one of claims 1 through 4, wherein the sealing means (25) has a combustion-chamber side pin (50) which protrudes into a combustion-chamber side opening (55) of the glow tube (10) and seals it, and the sealing means (25) includes a glow-tube-side base (60), which receives the heating coil (15).
 7. The glow plug (1) as recited in claim 6, wherein the heating coil (15) rests on the base (60).
 8. The glow plug (1) as recited in claim 6 or 7, wherein the base (60) includes a first projection (65) on the glow-tube side, which protrudes into the heating coil (15) and is in contact with the inner side (70) of the heating coil (15) on the combustion-chamber-side end.
 9. The glow plug (1) as recited in claim 6 or 7, wherein the base (60) itself protrudes into the heating coil (15) and is in contact with the inner side (70) of the heating coil (15) on the combustion-chamber-side end.
 10. The glow plug (1) as recited in claim 6 or 7, wherein the base (60) includes a second projection (75) on the glow tube side, which encloses the outside (80) of the heating coil (15) on its combustion-chamber-side end.
 11. A method for manufacturing an electrically heatable glow plug (1) for internal combustion engines, in which an electrically conductive heating coil (15) is introduced into a glow tube (10), wherein, before introduction of the heating coil (15) into the glow tube (10), which is initially open on its combustion-chamber-side end (20), the heating coil (15) is first connected on its combustion-chamber-side end to a sealing means (25), the sealing means (25) only protruding into the heating coil (15) if the heating coil (15) is attached to the sealing means (25) via an inner side (70) of the heating coil (15), for which purpose the sealing means (25) is essentially in contact with the inner side (70) of the heating coil (15) over the entire length protruding into the heating coil (15); and after introduction of the heating coil (15), together with the sealing means (25) positioned on the combustion-chamber side, into the glow tube (10), the glow tube is sealed on its combustion-chamber-side end (20) by the sealing means (25). 